Wireless communications based on identifying lower power nodes in heterogeneous network deployments

ABSTRACT

In a heterogeneous network deployment that includes one or more macro base stations and one or more low power nodes, a technique can be provided to encode network operational information using phase differences in synchronization signals transmitted by a network node. The synchronization signals may be one of the first signals that a user equipment (UE) attempts to locate when attempting to join a wireless network. The phase-encoded network operational information indicates to the UE where to locate a geometry indicator transmission from a low power node that is a part of the network, but is not the node that transmits the synchronization signals. The geometry indicator transmission may include identity information for the transmitting node and may be transmitted at a pre-determined nominal transmit power.

CROSS REFERENCE TO RELATED APPLICATIONS

This document claims the right of priority under 35 U.S.C. §119(a) andthe Paris Convention of International Patent Application No.PCT/CN2012/082334, filed on Sep. 28, 2012. The entire content of thebefore-mentioned patent application is incorporated by reference herein.

BACKGROUND

This document relates to cellular telecommunication systems, includingheterogeneous networks where one or more low-power nodes are deployed atleast partially within the coverage area of a macro base station.

Cellular communication systems are being deployed all over the world toprovide voice services, mobile broadband data services and multimediaservices. There is a growing need for cellular bandwidth due to variousfactors, including the continuous increase in the number of mobilephones such as smartphones that are coming on line and deployment of newmobile applications that consume large amounts of data, e.g., mobileapplications in connection with video and graphics. As mobile systemoperators add new mobile devices to the network, deploy new mobileapplications and increase the geographic areas covered by broadbandmobile services, there is an ongoing need to cover the operator'scoverage area with high bandwidth connectivity.

SUMMARY

The cellular bandwidth in a given coverage area can be increased by anumber of techniques, including improving the spectrum efficiency forthe point-to-point link and splitting communication cells into smallercells. In cell splitting, when the split cells become small and close toone another, the adjacent cell interferences can become significant andmay lead to the cell splitting gain saturation as the number of splitcells in a given area increases to above a certain number. Furthermore,nowadays it is increasingly difficult to acquire new sites to installbase stations and the costs for adding new base stations are increasing.These and other factors render it difficult to use cell-splitting tofulfill the increasing bandwidth demands.

This document describes technologies, among other things, for enablingimproved co-existence of low power nodes and macro base stations in aheterogeneous network deployment. The described technologies can beimplemented in ways that improve the available bandwidth in a givenheterogeneous network.

In one aspect, methods, systems and apparatus are disclosed forreceiving a first and a second synchronization signals, calculating aphase difference estimate between phases of the synchronization signals,determining a set of time-frequency resources based on the phasedifference estimate and configuring a geometry indicator receiver toreceive a geometry indicator signal transmission that uses resourcesfrom the set of time-frequency resources.

In another aspect, methods, systems and apparatus are disclosed fortransmitting, from a first node, a first synchronization signal using afirst set of transmission resources and transmitting, from the firstnode, a second synchronization signal using a second set of transmissionresource, such that a phase difference between the first synchronizationsignal and the second synchronization signal is indicative of a thirdset of transmission resources for use by a second node for transmittinga geometry indicator signal.

These and other aspects, and their implementations and variations areset forth in the drawings, the description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a wireless HetNet deployment scenario.

FIG. 2 depicts a wireless HetNet deployment that uses a geometryindicator.

FIG. 3 depicts a transmission resource allocation graph in which certainresource elements (REs) are assigned to transmission of a GeometryIndicator signal.

FIG. 4 depicts the allocation of REs to Geometry Indicator signaltransmissions.

FIG. 5 depicts transmission of primary and secondary synchronizationsignals having 180 degrees phase difference.

FIG. 6 depicts transmission of primary and secondary synchronizationsignals having a pre-determined phase difference.

FIG. 7 is a flow chart representation of a process of wirelesscommunications.

FIG. 8 is a block diagram representation of a wireless networkapparatus.

FIG. 9 is a flow chart representation of a process of wirelesscommunications.

FIG. 10 is a block diagram representation of a wireless networkapparatus.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The techniques described in this document are applicable to a wirelessnetwork serving one or more user equipment (UE) devices, such as amobile phone or a wireless communication device including a tablet orlaptop computer. The wireless network can be a heterogeneous network(HetNet) deployment having multiple tiers of communication nodes/basestations such as macro base stations and micro base stations. A macrobase station in such a HetNet has sufficiently high transmission powerto cover a large macro cell area while a micro base station is a lowpower node (LPN) that covers a smaller area within the larger macro cellarea.

The techniques disclosed in this document, in one aspect, can be used toencode network operational information using phase differences insynchronization signals transmitted by a network node. Thesynchronization signals may be one of the first signals that a userequipment (UE) attempts to locate when attempting to join a wirelessnetwork. The phase-encoded network operational information indicates tothe UE where to locate a geometry indicator transmission from a lowpower node that is a part of the network, but is not the node thattransmits the synchronization signals. The geometry indicatortransmission may include identity information for the transmitting nodeand may be transmitted at a pre-determined nominal transmit power. Inone advantageous aspect, the disclosed techniques therefore enable a UEnewly entering a wireless network, which does not have information abouttopology of the wireless network or whether low power base stations arepresent in the network or not, to quickly locate information about anylow power nodes and optionally adjust its uplink transmission powerand/or network admission process accordingly.

In another aspect, the disclosed techniques are useful to facilitatecontrolling power of signal transmission from a user equipment (UE) in aHetNet. the uplink power transmitted by the UE is controlled bytransmitting in the downlink direction information that allows the UE toestimate geometry of deployment, e.g., how close a low power node is tothe UE in comparison to a nearby macro cell base station, so that the UEcan set the proper uplink power to be sufficient for establishing areliable communication with the serving base station. This uplink powercontrol by UE in establishing communication with a serving base station,in one aspect, can be used to reduce interference from the UE to othernearby LPNs or UEs, thereby achieving higher data throughput for aHetNet deployment.

In some implementations, a macrocell base station can be used totransmit two different types of synchronization signals, e.g., primarysynchronization signal (PSS) and secondary synchronization signal (SSS),for UEs to identify the presence of a wireless cell and identify basicoperational details of the cell, respectively. These synchronizationsignals may use pre-defined signal structure and time-frequencyresources to allow a UE to quickly locate the synchronization signalswithout any user intervention. The disclosed techniques can beimplemented to encode information in such synchronization signals toenable UEs to locate, in the time-frequency plane of transmissionresources, time slots and subcarriers on which the geometry signals aretransmitted from among various possibilities.

As previously discussed, encoding geometry information that can belocated right after receiving synchronization signals and before layer 3or upper layer communication is established with the serving basestation, in one aspect, allows the network to control the uplinktransmission power used by the UE for subsequent network admissionprocess. Without the knowledge of the geometry information, the UE maytend to use maximum power for uplink transmission during the networkadmission stage. This maximum power operation of UE may inadvertentlydisrupt communication for other UEs and low power nodes that are nearthe UE because the UE is unaware of these nodes during the admissionprocess.

A Heterogeneous Network or HetNet includes a tier of macro base stationsforming a macro base station coverage and at least another tier ofmultiple low-power nodes (LPNs), or micro base stations. The coverage bythe LPN network tier is added onto the existing macro base stationscoverage area to improve the cellular coverage and the bandwidthavailable at each covered UE location. In some configurations, the macrobase station works as a master and the low power nodes work as slaves(e.g., follow transmission schedule controlled by the master) in orderto achieve certain advantages, e.g., better interference managements andresource allocation.

FIG. 1 shows one example of a HetNet deployment 100 that includes amacro base station 102, one or more low power nodes 104 for serving oneor more UEs 106 in the covered area. If a UE 106 is close to one lowpower node 104, its uplink transmit power may be unnecessarily highbefore the UE 106 establishes a connection with the network. Althoughthis high uplink transmit power from the UE 106 may be reduced uponestablishing the connection with the network since the process ofestablishing the network connect may require the UE 106 to lower itstransmit power by the uplink power control loop. This high transmitpower by UE 106 may cause some undesired effects. For example, the hightransmit power by UE 106 may generate significant uplink co-channelinterferences which can cause certain detriments to the uplink capacity.For another example, this unnecessary high transmit power by the UE 106may reduce the performance of or even saturate the receive chaincompletely at the particular low power node to which the UE 106 is closeand with which the UE 106 is establishing a network connection.

In one situation, where a UE 106 is close to one low power node, if themacro station scheduler could be aware of the UE's approach to the lowpower node, then the scheduler can assign the low power node to servethe UE 106 as soon as possible. In this way, the required transmit powerfor the downlink to the UE 106 can be lowered significantly by switchingfrom a relatively high transmit power in the downlink from the initialserving macro station to the UE 106 to a relatively low transmit powerin the downlink from the lower power node assigned by the macro stationscheduler. Power saving is similarly achieved for the uplink of the UE106, which is switched from a relatively high transmit power in theoriginal uplink from the UE 106 to the initial serving macro station toa relatively low transmit power in the new uplink from the UE 106 to thelower power node assigned by the macro station scheduler. The UE 106transmit power can be lowered significantly by switching from theinitial serving macro base station to the assigned lower power node.Consequently, both downlink and uplink interference generated by this UE106 to other UEs 106 in the network, which use the same frequencyresources at the same time, can be reduced and this reduction improvesthe overall system performance.

The awareness of UE's approach to a low power node may be based on theUE detecting or identifying the low power node's local ID and reportingthe detected ID to the macro base station afterwards. When a UE 106 isentering a new macro base station's coverage area for the first time,e.g., by roaming or by a power-on, the UE 106 has no way of knowing thepresence of other UEs 106 or low power nodes until the UE 106 completesnetwork admission process and begins to receive data and controlmessages from the macro base station. One reason being that low powernodes generally do not transmit synchronization signals that a new UE106 typically searches for to detect a wireless network.

In various wireless networks, such as Long Term Evolution (LTE) andWiMAX, synchronization signals are transmitted by the network, e.g., bymacro cell base station, for the benefit of user equipment or UE. Toassist a UE 106 to identify and join a network, a synchronizationsignal, called primary synchronization signal (PSS), is transmitted tothe UE 106 by the network. A UE can receive the PSS and extractinformation such as slot timing properties and identity the physicallayer. Often, a second synchronization signal, called secondarysynchronization signal (SSS), is transmitted by the network to the UE106 to allow the UE 106 to extract additional information such asidentification of the cell, structure of transmission frame and whethertime domain multiplexing (TDM) or frequency domain multiplexing (FDM) isused in the cell. Various existing wireless standards and HetNetdeployments do not specify any phase relationship between PSS and SSSand some allow for arbitrary phase relationships between PSS and SSS.

In this document, a technique is disclosed in which the phase differencebetween the primary synchronization signal (PSS) channel and thesecondary synchronization signal (SSS) channel is used as an indicationto the UE 106 about whether or not the UE 106 can receive a specialphysical signal located at a predefined resource element (RE) set, e.g.,time-frequency resources in orthogonal frequency domain multiplexing(OFDM) whose transmissions use time slots. In the examples providedbelow, the special physical signal can be a “geometry indicator” asfurther described below and is only transmitted to a UE 106 by the lowpower node but not by the macro base station.

In examples provided below, PSS and SSS phases can be usedinterchangeably and phase differences between other reference signalsmay also be utilized to signal geometry factor of RE locations asdescribed below.

In operation, a low power node (LPN) transmits its geometry indicatorsignal to its coverage area or microcell. Different LPNs transmit theirown respective geometry indicator signals. A UE 106 within the coveragearea of the LPN receives the LPN's geometry indicator signal. Inaddition, the macro base station that covers the LPN area transmits PSSand SSS signals to the UE 106. The UE 106 detects the phase differencebetween the received PSS and SSS and the UE 106 demodulates and decodesthe received geometry indicator signals located at the predefinedresource elements. Each geometry indicator signal received by the UE 106includes information about unique identity of a low power node thattransmits the received geometry indicator signal. The received geometryindicator signal also may provide additional information to the UE 106about how far the transmitting low power node is from the UE 106. Insome embodiments, based on the detected phase difference (e.g., whetherthe value is close to 45, 90, 180 or 225 degrees), the UE searches themost likely low power node ID within a pre-defined ID set.

In some implementations, in order to save the UE battery life, if nophase difference is detected between PSS and SSS, the UE could stop thedemodulation and decoding of the received geometry indicator signalslocated at the predefined resource elements. After the low power node IDis identified based on the received geometry indicator signal, the UEreports the ID to the macro base station after the UE establishes theconnection to the network.

Example embodiments using Long Term Evolution (LTE) deploymentscenarions are discussed in the specific examples below, but theapplication of the disclosed techniques is not limited to LTE, and canbe used in other types of cellular HetNet communication systems.Furthermore, the terms used in this specification are generallyconsistent with their usage in the currently published versions of 3GPPdocuments TS 36.211 (version 10.5) and TS 36.212 (version 10.6), therelevant portions of which are incorporated in this document byreferences.

With reference to FIG. 2, the operation of a HetNet 200 that uses ageometry indicator is further discussed.

(1) Primary synchronization signal PSS (201) and secondarysynchronization signal SSS (202) are transmitted only by the macro basestation 106. A low power nodes 104 is not used to transmit the PSS andSSS signals. For example, in LTE networks, PSS/SSS 201, 202 are locatedat time slot 0 and slot 10 respectively in one radio frame.

(2) SSS is only transmitted at the macro base station. The low powernodes are not used to transmit SSS signals. The SSS transmitted by themacro base station is located at slot 0 and slot 10, respectively, inone radio frame. Furthermore, a phase difference, as further describedbelow, between SSS and PSS is applied on SSS.

With reference to FIG. 5, in some implementations, the phase differencebetween SSS and PSS is set to it radians, or 180 degrees. In someimplementations, the 180 degrees phase difference would indicate the UE106 to demodulate and decode the low power node ID carried by somepredefined resource elements. In some implementation, a range of phasedifference values around 180 degrees may be considered to be 180degrees. For example, in one implementation, if a phase differenceestimate is within 178 to 182 degrees, then it would be considered to beeffectively equal to 180 degree difference. Of course, depending on thetrade-off between desired sensitivity and probability of falsedetection, other ranges (e.g., plus/minus 5 degrees) may be used.

With reference to FIG. 6, the phase difference is chosen among the Dpositions in the unit circle, e.g., 4 positions, and each position iscorresponding a predefined resource element ID set where the UE cansearch and find the most likely ID number. For example, in someimplementations, the UE may maintain a pre-determined set of discretephase values—e.g., 45, 90, 135 and 180 degrees. The UE may compare thecalculate phase estimate and determine the closest phase value from theset. For example, calculated phase value of 50 degrees may be mapped tothe closest value 45 degrees, and so on. Other mappings, e.g., equalrange partitions, may also be used.

(3) Geometry Indicator 204 is only transmitted by the low power nodes104:

One embodiment example is as follows:

Sequence

a) Only one sequence indicating the geometry indicator for all LPNs 104.And the geometry indicator could be a predefined 32-bit sequence. Forexample, one of the control frame indicator (CFI) sequences can bereused as the geometry indicator, for example, the first CFI sequence:<0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1>  Eq(1)

b) There are several predefined sequences and each sequence correspondsto the LPN ID or group ID. For example, all of the CFI sequences can bereused as the geometry indicator.

Time-Frequency Plane Location

In LTE, in one radio frame (10 ms), there are 20 Resource Elements (REs)unused at the same orthogonal frequency domain multiplexing (OFDM)symbols as PSS and SSS 202 located. Therefore 16 REs of them is used forthe geometry indicator 204. And in order to have less impact on thesynchronization channels, the rest 4 REs are used to separate geometryindicator and the synchronization channels. This arrangement is depictedin FIG. 3.

With reference to FIG. 3, REs are plotted along time axis (horizontal)and frequency axis (vertical) with RE group 302 and 304 showing theunused subcarriers in OFDM symbols used by primary and secondarysynchronization signals. The time-frequency plane mapping oftransmission resources in the form of REs. Each RE represents asubcarrier of the OFDM signal and a duration of time or a time slot thatthe signal is transmitted in.

FIG. 4 shows an enlarged view of RE groups 302 and 304. REs 402correspond to the REs usable by geometry indicator signals. REs 404 areused by PSS and REs 406 are used by SSS. REs 408 can be optionally usedto provide separation between PSS/SSS and geometry signal transmissions.In one beneficial aspect, REs 408 help mitigate any backwardcompatibility issue with UEs that are expecting no energy transmissionin the REs 402.

As can be seen from FIG. 4, when, e.g., a geometry indicator uses twoREs out of possible 8 REs 402, several possible assignments of 2 REsfrom 8 available REs 402 are possible. Therefore, the phase differencebased signaling of which two REs are used, in one aspect, avoids thecomplexity of the UE 106 having to decode all possible combinations ofREs. For example, in some implementations, a 45 degree phase differencemay indicate that two REs farthest away from the PSS/SSS are used forcoding LPN IDs, while a 90 degree phase difference may indicate that 4farthest REs are used. Other mappings between phase differences andwhich (and how many) REs from the possible set of REs is used fortransmitting geometry indicator are possible.

Modulation

The 32-bit sequence is QPSK modulated to be carried on the 16 REs.

Another embodiment example is:

The geometry factor carries L bits LPN ID. The L-bit LPN ID is at firstencoded into M bits, then M bits are modulated into Q symbols, and the Qsymbols are finally mapped to Q physical REs whose relative positions toPSS/SSS are fixed and known by UEs. And if those REs are not located inthe same OFDM symbols in the time domain as PSS or SSS, then P extrareference symbols are defined and allocated in these Q physical REs tofacilitate the UE's demodulation.

(4) UE searches PSS signal as normally

(5) When UE finds PSS, and performs SSS detection as normally. Once UEobtains the synchronization to the found cell, UE compares the phasedifference between SSS and PSS.

(6) According to the detected phase difference, it detects/decodes thegeometry indicator at the same OFDM symbols as the found synchronizationchannels.

(7) In the embodiment example one, if the detected phase difference isπ, then it means that the UE needs to demodulate and decode the geometryfactor located at the predefined physical REs.

(8) In the embodiment example two, UE chooses the most likely phasedifference among the predefined D values, and finds the correspondingpredefined ID set, then demodulates and decodes the received signalswhich carries the low power node ID, and then finally finds the mostlikely ID among the predefined ID set.

(9) UE can also report the decoded LPN ID to the network actively,periodically or at the request by the network. For example, the LPN IDcan be an auxiliary input to the network for locating the UE.

In some implementations, multiple LPNs may coordinate with each other toform a group that is represented by a group ID. These LPNs maycoordinate to transmit an identical geometry indicator signal in the REs402 using the shared group ID for identification. The power of geometryindicator signal may be adjusted downwards so that the additive effectof transmissions from all LPNs at the UE does not exceed apre-determined threshold.

In a typical deployment scenario, the LPNs may be deployed to facilitatethe operation of a UE in a range between 1 meter to 40 meters. Intypical deployment scenarions, based on the path characteristics, UEoperation may result in a 20 dB to 6 dB backoff in power from the peakrandom access preamble transmission power.

FIG. 7 is a flow chart representation of a process 700 for operating awireless device in a wireless network. At 702, a first synchronizationsignal is received from a first node. The first node can be, e.g., amacro base station (macrocell base station). The first synchronizationsignal can be, e.g., PSS (also sometimes abbreviated as P-SS).

At 704, a second synchronization signal is received from the first node.The second synchronization signal can be, e.g., SSS (also sometimesabbreviated as S-SS).

At 706, a phase difference estimate between phases of the firstsynchronization signal and the second synchronization signal iscalculated. The estimation of phases of signals and comparing the phasescan be implemented in various ways.

At 708, a set of time-frequency resources is determined based on thephase difference estimate. For example, as previously discussed, 180degree phase difference may indicate a specific pre-determined set ofall possible REs being used for geometry indicator transmission.Similarly, as previously discussed, a number of discrete phasedifference values may map to a different subset of REs.

At 710, a geometry indicator receiver is configured, when a magnitude ofthe phase difference estimate is greater than a first threshold, toreceive a geometry indicator signal transmission that uses resourcesfrom the set of time-frequency resources. In some embodiments, when thephase difference is below a threshold (e.g., 2 degrees) it is consideredto be equivalent to no phase difference for the purpose of determiningREs for geometry indicator.

As previously discussed, the geometry indicator signal may includeidentity of the low power node that transmitted the signal. Using thesignal power in the geometry indicator signal, the wireless device mayestimate an amount by which to backoff its uplink transmission powerduring the network admission process. The wireless device may alsocommunicate to the network the identity of the low power node receivedin the geometry indictor signal. In one aspect, this may allow thenetwork to identify location of the wireless device concurrently withthe admission process, thereby guiding the wireless device to operateaccordingly in the macrocell or microcell.

FIG. 8 is a block diagram representation of a portion of a wirelesscommunications apparatus. The module 802 is for receiving a firstsynchronization signal from a first node. The module 804 is forreceiving a second synchronization signal from the first node. Themodule 806 is for calculating a phase difference estimate between phasesof the first synchronization signal and the second synchronizationsignal. The module 808 is for determining a set of time-frequencyresources based on the phase difference estimate. The module 810 is forconfiguring a geometry indicator receiver, when a magnitude of the phasedifference estimate is greater than a first threshold, to receive ageometry indicator signal transmission that uses some resources from theset of time-frequency resources. The apparatus 800 and modules 802, 804,806, 808 and 810 can be further configured to perform one or moretechniques described in this document.

FIG. 9 is a flowchart representation of a process 900 of wirelesscommunications. At 902, a first synchronization signal is transmittedusing a first set of transmission resources. The first synchronizationsignal may be, e.g., PSS. The first set of transmission resources maybe, e.g., slot 0/10 REs as previously discussed. At 904, a secondsynchronization signal (e.g., SSS) is transmitted using a second set oftransmission resource (e.g., previously discussed slot 0/10 REs forSSS), such that a phase difference between the first synchronizationsignal and the second synchronization signal is indicative of a thirdset of transmission resources for use by a second node for transmittinga geometry indicator signal. As previously discussed, in someimplementations, the phase difference can only be equal to one of apre-determined set of values. In some implementations, the geometryindicator signal may include information that uniquely identifies a nodethat transmits the geometry indicator signal. Various uses and featuresof the geometry indicator signal have been previously described in thisdocument.

FIG. 10 is a block diagram representation of a portion of a wirelesscommunications apparatus 1000. The module 1002 is for transmitting afirst synchronization signal using a first set of transmissionresources. The module 1004 is for transmitting a second synchronizationsignal using a second set of transmission resource, such that a phasedifference between the first synchronization signal and the secondsynchronization signal is indicative of a third set of transmissionresources for use by a second node for transmitting a geometry indicatorsignal. The apparatus 1000 and modules 1002, 1004 may further beconfigured to implement some of the techniques disclosed in thisdocument.

As previously discussed, a wireless communication system according tothe present document includes a macrocell base station, a microcell basestation (low powered node) and at least one UE. The macrocell basestation can be configured to transmit a primary synchronization signal(PSS) and a secondary synchronization signal (SSS) such that a phasedifference between the PSS and the SSS is indicative of location ofresource elements used by a geometry indicator in a time-frequencyresource plane (e.g., FIG. 4). The microcell base station can beconfigured to refrain from transmitting PSS and SSS and to transmit thegeometry indicator using the resource elements indicated by themacrocell base station. The UE, or the mobile station, can be configuredto receive the PSS and the SSS, locate and successfully receive thegeometry indicator using the location information indicated by the phasedifference, and report an identity of the microcell base station to themacrocell base station.

It will be appreciated that various techniques are disclosed forimproved operation of macro and micro (low power) nodes in aheterogeneous network are disclosed.

It will further be appreciated that the disclosed techniques enablereduction in complexity of implementation at a UE or mobile stationbecause REs at which to locate geometry indicator is signaled via phasedifference between two synchronization signals received from the macrocell base station.

The disclosed techniques enable operation of a heterogeneous network inwhich a new wireless device or UE is admitted to the network without thedevice having to use full uplink power during admission, which maycreate interference to the operation of other wireless devices or lowpower nodes nearby.

The disclosed and other embodiments and the functional operationsdescribed in this document can be implemented in digital electroniccircuitry, or in computer software, firmware, or hardware, including thestructures disclosed in this document and their structural equivalents,or in combinations of one or more of them. The disclosed and otherembodiments can be implemented as one or more computer program products,i.e., one or more modules of computer program instructions encoded on acomputer readable medium for execution by, or to control the operationof, data processing apparatus. The computer readable medium can be amachine-readable storage device, a machine-readable storage substrate, amemory device, a composition of matter effecting a machine-readablepropagated signal, or a combination of one or more them. The term “dataprocessing apparatus” encompasses all apparatus, devices, and machinesfor processing data, including by way of example a programmableprocessor, a computer, or multiple processors or computers. Theapparatus can include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them. A propagated signal is an artificially generated signal, e.g.,a machine-generated electrical, optical, or electromagnetic signal, thatis generated to encode information for transmission to suitable receiverapparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this document can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of non volatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices; magnetic disks, e.g., internal hard disks or removable disks;magneto optical disks; and CD ROM and DVD-ROM disks. The processor andthe memory can be supplemented by, or incorporated in, special purposelogic circuitry.

While this document contains many specifics, these should not beconstrued as limitations on the scope of an invention that is claimed orof what may be claimed, but rather as descriptions of features specificto particular embodiments. Certain features that are described in thisdocument in the context of separate embodiments can also be implementedin combination in a single embodiment. Conversely, various features thatare described in the context of a single embodiment can also beimplemented in multiple embodiments separately or in any suitablesub-combination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asub-combination or a variation of a sub-combination. Similarly, whileoperations are depicted in the drawings in a particular order, thisshould not be understood as requiring that such operations be performedin the particular order shown or in sequential order, or that allillustrated operations be performed, to achieve desirable results.

Only a few examples and implementations are disclosed. Variations,modifications, and enhancements to the described examples andimplementations and other implementations can be made based on what isdisclosed.

What is claimed is:
 1. A method of operating a wireless device in awireless network, comprising: receiving a first synchronization signalfrom a first node; receiving a second synchronization signal from thefirst node; calculating a phase difference estimate between phases ofthe first synchronization signal and the second synchronization signal;determining a set of time-frequency resources based on the phasedifference estimate; and configuring a geometry indicator receiver, whena magnitude of the phase difference estimate is greater than a firstthreshold, to receive a geometry indicator signal transmission that usesresources from the set of time-frequency resources.
 2. The method ofclaim 1, wherein: the first node comprises a macro-area node, the firstsignal comprises a primary synchronization signal, and the second signalcomprises a secondary synchronization signal.
 3. The method of claim 2,wherein the primary and secondary synchronization signals usetime-frequency resources that are different from the set oftime-frequency resources.
 4. The method of claim 3, wherein the set oftime-frequency resources fit within the same orthogonal frequency domainmultiplexing (OFDM) symbols as time-frequency resources used by theprimary synchronization signal and the secondary synchronization signal.5. The method of claim 1, further comprising: transmitting to the firstnode, when a geometry indicator signal is successful received in the setof time-frequency resources, a report comprising an identity of a secondnode that transmitted the geometry indicator signal.
 6. The method ofclaim 5, wherein: the second node includes a micro cell node.
 7. Themethod of claim 1, wherein: a nominal transmission power of the geometryindicator signal is less than nominal transmission powers of the firstand the second synchronization signals.
 8. The method of claim 1,wherein the determining the set of time-frequency resources based on thephase difference estimate comprises checking whether the phasedifference estimate is within a second threshold of 180 degrees.
 9. Themethod of claim 1, wherein the determining the set of time-frequencyresources based on the phase difference estimate comprises determining,from a list of phase difference values, a candidate phase differencevalue that is closest to the phase difference estimate.
 10. The methodof claim 1, further comprising, powering down the geometry indicatorreceiver, when the magnitude of the phase difference estimate is equalto or less than the first threshold.
 11. A wireless device operable in aheterogeneous wireless network that includes a macrocell base stationand a microcell base station, comprising: a first synchronization signalreceiver that receives a first synchronization signal; a secondsynchronization signal receiver that receives a second synchronizationsignal from the macrocell base station; a phase difference estimatorthat calculates a phase difference estimate between phases of the firstsynchronization signal and the second synchronization signal; a resourcedeterminer that determines a set of time-frequency resources based onthe phase difference estimate; and a receiver configurator thatconfigures a geometry indicator receiver, when a magnitude of the phasedifference estimate is greater than a first threshold, to receive ageometry indicator signal transmission that uses resources from the setof time-frequency resources.
 12. The device of claim 11, wherein: thefirst signal comprises a primary synchronization signal (PSS) having afirst nominal power level, and the second signal comprises a secondarysynchronization signal (SSS) having a second nominal power level. 13.The device of claim 12, wherein the PSS and SSS use time-frequencyresources that are different from the set of time-frequency resources.14. The device of claim 13, wherein the set of time-frequency resourcesfit within the same orthogonal frequency domain multiplexing (OFDM)symbols as time-frequency resources used by the PSS and SSS.
 15. Thedevice of claim 11, further comprising: a report transmitter thattransmits to the macrocell base station, when a geometry indicatorsignal is successful received in the set of time-frequency resources, areport comprising an identity of a transmission node that transmittedthe geometry indicator signal.
 16. The device of claim 15, wherein: thetransmission node includes the micro cell node.
 17. The device of claim11, wherein: a nominal transmission power of the geometry indicatorsignal is less than nominal transmission powers of the PSS and the SSS.18. The device of claim 11, wherein the resource determiner comprises achecker that checks whether the phase difference estimate is within asecond threshold of 180 degrees.
 19. The device of claim 11, wherein theresource determiner comprises a lookup determiner that associates, froma list of phase difference values, a candidate phase difference valuethat is closest to the phase difference estimate.
 20. The device ofclaim 11, wherein the receiver configurator further, powers down thegeometry indicator receiver, when the magnitude of the phase differenceestimate is equal to or less than the first threshold.
 21. Anon-transitory, processor-readable medium having processor-executableinstructions stored thereon, the instructions, when executed, causing aprocessor to implement a wireless communications method, comprising:receiving a first synchronization signal from a first node; receiving asecond synchronization signal from the first node; calculating a phasedifference estimate between phases of the first synchronization signaland the second synchronization signal; determining a set oftime-frequency resources based on the phase difference estimate; andconfiguring a geometry indicator receiver, when a magnitude of the phasedifference estimate is greater than a first threshold, to receive ageometry indicator signal transmission that uses resources from the setof time-frequency resources.
 22. A method of wireless communications,comprising: transmitting, from a first node, a first synchronizationsignal using a first set of transmission resources; transmitting, fromthe first node, a second synchronization signal using a second set oftransmission resource, such that a phase difference between the firstsynchronization signal and the second synchronization signal isindicative of a third set of transmission resources for use by a secondnode for transmitting a geometry indicator signal; wherein the third setof transmission resources occupy non-overlapping time-frequency resourceelements in a same time slot as the first set of transmission resourcesor the second set of transmission resources.
 23. The method of claim 22,wherein the phase difference can only be equal to one of apre-determined set of values.
 24. The method of claim 22, wherein thegeometry indicator signal includes information uniquely identifying thesecond node.
 25. A wireless communications apparatus, comprising: afirst synchronization signal transmitter that transmits a firstsynchronization signal using a first set of transmission resources; asecond synchronization signal transmitter that transmits a secondsynchronization signal using a second set of transmission resource, suchthat a phase difference between the first synchronization signal and thesecond synchronization signal is indicative of a third set oftransmission resources for use by a transmission node for transmitting ageometry indicator signal; wherein the third set of transmissionresources occupy non-overlapping time-frequency resource elements in asame time slot as the first set of transmission resources or the secondset of transmission resources.
 26. The apparatus of claim 25, whereinthe phase difference can only be equal to one of a pre-determined set ofvalues.
 27. The apparatus of claim 25, wherein the geometry indicatorsignal includes information uniquely identifying the second node.
 28. Awireless communication network, comprising: a macrocell base stationthat transmits a primary synchronization signal (PSS) and a secondarysynchronization signal (SSS) such that a phase difference between thePSS and the SSS is indicative of location of resource elements used by ageometry indicator in a time-frequency resource plane; a microcell basestation configured to: refrain from transmitting PSS and SSS; andtransmit the geometry indicator using the resource elements indicated bythe macrocell base station; and a mobile station configured to: receivethe PSS and the SSS; locate and successfully receive the geometryindicator using the location information indicated by the phasedifference; and report an identity of the microcell base station to themacrocell base station.
 29. The wireless communication network of claim28, wherein the PSS and the SSS use time-frequency resources that aredifferent from the set of time-frequency resources.
 30. The wirelesscommunication network of claim 28, wherein the PSS and the SSS usetime-frequency resources use the set of time-frequency resources.